A number of techniques exist to increase the surface hardness of metallic elements; a metal film can be placed on the elements which is harder than the metal constituting it, such as an element in the form of plasma, or work-harden the surface of the element by means of shot blasting which introduces superficial compression stresses. In the case of shot blasting, debris of projectiles are frequently incrusted on the surface of the element and form there indents whose bottom is often sharp and constitutes a start of rupture caused by metal fatigue of the element which may impair the benefits of the surface hardness obtained.